1. Field of the Invention
The present invention relates to an apparatus and method for inducing an electrochemical reaction on an article. More particularly, the present invention relates to electrodepositing material on semiconductor components by attaching the semiconductor components on a cathode immersed in an appropriate electrolyte wherein a wire mesh anode rotates about the cathode during electrodeposition.
2. State of the Art
Semiconductor wafers, substrates, and printed circuit boards (collectively hereinafter "semiconductor substrates") are often coated with various materials, such as metals which are etched in later semiconductor fabrication processes to form components on the semiconductor substrates. Techniques for coating semiconductor substrates include electrodeposition, electron beam evaporator deposition, chemical vapor deposition, sputter deposition, and the like. Electrodeposition has become a commonly used technology.
Electrodeposition is a process which deposits a thin film of material, such as metal or metal alloy, on an article. In electrodeposition, as shown in prior art FIG. 10, an article 202 is placed in a tank 204 containing an appropriate deposition solution, such as electrolyte solution 206, which contains ions 208 of the metal to be deposited on the article 202. The article 202 forms a cathode or is in electrical contact with a cathode 210 which is immersed in the electrolyte solution 206. The cathode 210 is connected to a negative terminal 212 of a power supply 214. A suitable anode 216 is also immersed in the electrolyte solution 206 at an appropriate distance from the cathode 210 and is connected to a positive terminal 218 of the power supply 214. The power supply 214 generates an electrical current which flows between the anode 216 and the cathode 210 through the electrolyte solution 206. The electrical current causes an electrochemical reaction at the surface of the article 202 which results in the metal ions 208 in the electrolyte solution 206 being deposited on the article 202.
With semiconductor components, it is desirable to deposit the metal film with a uniform thickness across the article and with uniformity of composition of the metal(s) and/or other compounds forming the metal film. However, the electrodeposition process is relatively complex and various naturally occurring forces may result in a degradation in the electrodeposition process. The electrical current or flux path between the anode and the cathode should be uniform without undesirable spreading or curving to ensure uniform deposition. Additionally, since the metal ions in the deposition solution are deposited on the article, the deposition solution becomes depleted of metal ions which degrades the electrodeposition process. Therefore, suitable controls are required to introduce metal ions into the deposition solution in order to maintain consistency.
U.S. Pat. No. 5,516,412 issued May 14, 1996 to Andricacos et al. (the '412 patent) relates to an electrodeposition cell having a rack for vertically supporting a silicon substrate to be electrodeposited. A paddle is disposed within the electrodeposition cell for agitating an electrolyte solution within the cell to maintain a uniform distribution of deposition material within the electrolyte solution. Furthermore, the '412 patent teaches that the rack can be designed to be removable for automated handling. Although the '412 patent addresses the control issues discussed above, the rack assembly disclosed is not conducive to high-volume manufacturing. Furthermore, the '412 patent does not teach or suggest any means for improving the deposition on the silicon substrate by the movement of either the anode or cathode.
U.S. Pat. No. 4,696,729 issued Sep. 29, 1987 to Santini and U.S. Pat. No. 5,198,089 issued Mar. 30, 1993 to Brueggman both relate to an electrodeposition cell having a cathode assembly which is vertically mounted and holds a plurality of semiconductor substrates to be coated, and an anode which is also vertically mounted adjacent to the cathode assembly. The deposition solution is pumped upward between the anode and the cathode to produce a laminar flow across the surface of each wafer. However, both patents lack a means for insuring uniform distribution of deposition material within the deposition solution.
Systems which can be used for electrodeposition can also be used for electropolishing and electroetching. For example, U.S. Pat. No. 5,096,550 issued Mar. 17, 1992 to Mayer et al. (the '550 patent) teaches attaching an article to a rotating anode positioned horizontally face down in a polishing or etching bath. However, the '550 patent teaches only the motion of the cathode and since the articles are attached one at a time in the anode, the apparatus of the '550 patent is not conducive to high-volume manufacturing.
In most electrodeposition techniques, the wafers are attached to the cathode. The attachment of the wafers to the cathode can lead to significant problems, especially as the wafer quantities are increased within a single batch, wherein control of the thickness of the material on the wafer becomes a problem. The problem of material thickness control is brought about by the non-uniformity of metal ions and less uniform current density in the electrolyte solution.
It is desirable to provide highly uniform thickness and composition of deposition material on an electrodeposited article or to uniformly polish or etch an article. Furthermore, it is also desirable to do so in an apparatus capable of high-volume manufacturing, preferably using automated handling equipment.